This invention relates to a new family of olefin, in particular ethylene oligomerization catalysts based upon phenoxide complexes of transition metals and methods for their use.
Alpha-olefins, especially those containing 4 to about 20 carbon atoms, are important items of commerce, with about 1.5 million tons reportedly being produced in 1992. The alpha-olefins are used as intermediates in the manufacture of detergents, as monomers (especially in linear low density polyethylene), and as intermediates for many other types of products. As a consequence, improved methods of making these compounds are of interest.
Most commercially produced alpha-olefins are made by the oligomerization of ethylene, catalyzed by various types of compounds, see for instance B. Elvers, et al., Ed. Ullmann""s Encyclopedia of Industrial Chemistry, Vol. A13, VCH Verlagsgesellschaft mbH, Weinheim, 1989, p. 243-247 and 275-276, and B. Cornils, et al., Ed., Applied Homogeneous Catalysis with Organometallic Compounds, A Comprehensive Handbook, Vol. 1, VCH Verlagsgesellschaft mbH, Weinheim, 1996, p. 245-258. The major types of commercially used catalysts are alkylaluminum compounds, certain nickel-phosphine complexes, and a titanium halide with a Lewis acid such as AlCl3. In all of these processes significant amounts of branched and/or internal olefins and/or diolefins, are produced. Since in most instances these are undesired, and often difficult to separate from the desired linear alpha-olefins, minimization of these byproducts is desirable.
Examples of new ethylene oligomerization catalysts which produce high purity alpha-olefins have recently appeared. Brookhart recently developed iron-based catalysts, which produce either high molecular weight HDPE or high purity xcex1-olefins, depending on the extent of steric effects of ligand substituents. (Small, B. L.; Brookhart, M. J. Am. Chem. Soc. 1998, 120, 7143; U.S. Pat. No. 6,103,946.) These iron-based ethylene oligomerization catalysts exhibit very high catalytic activities and produce highly pure alpha-olefins. However, use of these catalysts to produce alpha-olefin comonomers in situ for polymerization by, for example, metallocene catalysts, could be confounded by potential incompatibilities between the iron and metallocene catalysts.
Bazan utilized electronic control of molecular weight in his studies with Zr-boratabenzene catalysts. (Rogers, J. S.; Bazan, G. C.; Sperry, C. K. J. Am. Chem. Soc. 1997, 119, 9305.) B-Ph boratabenzene complexes were observed to produce polyethylene, but the less electron-rich B-OMe boratabenzene analog catalyzed ethylene oligomerization. By incorporating an electron withdrawing substituent on boron, the electrophilicity of the catalyst was increased which resulted in an increased xcex2-H elimination rate and lower molecular weight product. Like the Brookhart Fe catalyst, Bazan""s boratabenzene catalyst exhibits extremely high selectivity for xcex1-olefin production. The catalytic activity of the boratabenzene-Zr catalyst is much lower than that required for commercial operation in a tandem oligomerization/polymerization process using a metallocene polymerization catalyst.
Transition metal complexes of salicylimine ligands have recently been reported which are extremely active polymerization catalysts. Grubbs et al (Organometallics, Vol 17, 1988 page 3149-3151; WO 98/42664) disclose that nickel (II) salicylaldiminato complexes, combined with B(C6F5)3, reacted with ethylene to form polyethylene with MW=49,500.
Ethylenebis(salicylideneiminato)zirconium dichloride combined with methyl alumoxane deposited on a support and unsupported versions were used to polymerize ethylene by Repo et al in Macromolecules 1997, 30, 171-175.
EP 241,560 A1 (Sumitomo) discloses alkoxide ligands in transition metal catalyst systems.
EP 0 874 005 A1 discloses salicylimine compounds for use as polymerization catalysts.
WO 00/37512 discloses a family of olefin polymerization catalysts based upon phenoxide complexes of transition metals.
In all of the above cases, salicylimine transition metal complexes reacted with ethylene to produce polyethylene, not ethylene oligomers or alpha-olefins. Described herein is a new class of salicylimine-based ethylene oligomerization catalysts having high activity and high selectivity for alpha-olefin. One application of these catalysts is their use in a mixed catalyst system which produces linear low density polyethylene (LLDPE) using only ethylene feedstock.
This invention relates to a process to produce alpha-olefins comprising contacting ethylene with a catalyst system comprising an activator and one or more metal catalyst compounds represented by the following formula: 
wherein
R3, R4, R5, R8, R9 and R10 may each independently be hydrogen, a halogen, a heteroatom containing group or a C1 to C100 group, provided that at least one of these groups has a Hammett "sgr"p value (Hansch, et al Chem. Rev. 1991, 91, 165) greater than 0.20;
R2 and R7 may each independently be alkyl, aryl or silyl groups preferably tertiary alkyl, tertiary silyl or aryl groups;
R1 and R6 may each independently be an alkyl group, an aryl group, an alkoxy group, or an amino group, preferably a C1 to C5 primary alkyl group;
N is nitrogen;
H is hydrogen;
O is oxygen;
M is a group 4 transition metal; and
each X may each independently be an anionic ligand such as halide, alkyl, aryl, hydride, carboxylate, alkoxide or amide, or a dianionic ligand, such as a dialkoxide or diamide.
These catalyst compounds may be activated with activators including alkyl aluminum compounds (such as diethylaluminum chloride), alumoxanes, modified alumoxanes, non-coordinating anions, non-coordinating group 13 metal or metalliod anions, boranes, borates and the like.
This invention further relates to the production of polymer by introducing ethylene, a polymerization catalyst and a catalyst system as described above into a polymerization reactor. Preferably the polymer produced is an ethylene homopolymer or an ethylene co-polymer.